Rockglaciers

Global climatic change and sustainable development are key words in the discussion of the future of the geosystems on Earth. Both concepts are extremely important for the future development of high mountain systems in which the high mountain environments or cryogenic belts, e.g., the landscapes above the timberline, are especially endangered. Unfortunately, our knowledge of these geosystems is very limited. It is, therefore, essential to define diagnostic landforms which are important as indicators for the geoecology of these systems and for monitoring possible climatic changes in mountain belts. This requires an extensive geomorphic knowledge of the landforms accepted as diagnostic. Otherwise the derived information may be confusing or wrong and of no help for monitoring climate changes or for establishing a more considered and sustainable use of these geosystems.

Active, i.e., presently moving rockglaciers (cf. Figs. 1.1’1.4), form an important and fascinating landform in alpine (high mountain) environments. They indicate alpine or mountain permafrost belts, and, thus, possess a high geodynamic and geoecologic information value. Unfortunately, discussions about rockglaciers are often very confusing. Some students, influenced by semantics, believe that rockglaciers are just debris-covered glaciers (Lliboutry 1965, 1986; Klaer 1974; Whalley 1974a); others accept features of quite different origin as rockglaciers. Often, glacial geomorphologists or glaciologists favor a glacial origin; workers in the field of permafrost believe in a periglacial genesis. Those who subscribe to neither of these groups have proposed that there are some types of rockglaciers which belong to the periglacial, and other types that belong to the glacial realm (White 1971b; Potter 1972). The term “continuum” (Johnson 1974, 1983; Corte 1987a; Giardino and Vitek 1988; Chap. 8) is highly favored in this context.

The landform which is today called a rockglacier has been known to scientists for more than a century. With changing models of explanation, the term describing it has been altered several times. In addition, when terms from our everyday language are used, misunderstandings are prone to occur, because - if the correct definition is not known - these terms may lead to the introduction of models which are inappropriate to the phenomena under discussion.

Rockglaciers have been described in all major high mountain systems of the world (cf. Chap. 5). According to the topographic, climatic and other influences on the creep of mountain permafrost, a wide variety of forms exist. The sizes and forms of active rockglaciers may be quite different, not only in different mountain systems but also locally. Nevertheless, a basic description can be given; a genetic approach, however, which has often been connected with a discussion of size and form in the past, is not intended.

According to the definitions in the foregoing chapters, active rockglaciers are the visible expression of the creep of supersaturated mountain permafrost. The process combination which leads to the formation of an active rockglacier is controlled by thermal boundaries that allow the formation of ice-rich permafrost in unconsolidated materials in mountain terrain. Material properties (ice type, etc.) are clearly of minor importance. A taxonomy or a classification of rockglacier types has, therefore, to follow certain rules: it should avoid unnecessary genetic and material complications, it should not contain special hypotheses, and it should be descriptive and easily applicable.

Active rockglaciers have been reported in all major high mountain systems of the world, but still today a systematic summary of their distribution is missing. An extremely valuable study on the distribution of rockglaciers in Europe and North America has been published by Höllermann (1983a).

Rockglaciers are two-layered phenomena according to texture and to temperature. The difference in texture is visible even at the front slopes where, under the bouldery upper layer, fine-grained material appears. Based on textures, it seems convenient to differentiate between the outer, bouldery rockglacier mantle and the inner rockglacier core. The distinction according to temperature is related to the active layer which is unfrozen in summer and the permanently frozen inner part. The two distinctions are normally not congruent, but most parts of the rockglacier core are frozen and contain ice. If only the “normal” pore volume of unconsolidated material in an unfrozen state of ca. 30’40 vol% is filled with ice, this part of the core is ice-saturated. If the whole core or parts contain more ice by volume than this “normal” pore space, then these parts are ice-oversaturated or ice-supersaturated.

The movement of rockglaciers has caused quite a lot of speculation. Theoretically, a huge mass of debris can be moved by a number of different processes (Johnson 1987). A discussion of these various theoretical possibilities has to be based on information of measured velocities and on the geometry of the rockglacier movement. This is possible today, because measurements have been carried out for more than 70 years on different rockglaciers around the world. Even if the methods used are extremely different, quite a good picture of the geometry of the surface movement of rockglaciers has been developed.

In the discussion of rockglacier genesis, three terms, Chaos - Continuum - Order are of greatest importance. In the literature, a large number of contradicting hypotheses have been proposed: this is chaos. A number of proposals have been made to clarify this situation. The logical first hypothesis would include rockglaciers in a group of broadly similar-looking landforms (ranging from glacial and landslide deposits to real rockglaciers under other names) as a continuum (Johnson 1974, 1983; Corte 1987a; Giardino and Vitek 1988). This approach is not really helpful. It is correct (Giardino and Vitek) that relief forms a continuum which can be considered at different scales and with different geometric or geomorphic intentions, but it seems unwise to use the continuum aspect to mask clear differences. The only way to create order as a basis for a better understanding is a process-oriented definition, “because form is a response to a process operating over time” as Giardino and Vitek (1988) state. Based on the definition in Chapter 1, the genesis and the phenotypes of active (Sect. 8.1.1), inactive (Sect. 8.1.2) and relict (Sect. 8.1.3) rockglaciers will be discussed first. In comparison to this, all physiognomic similar forms will be discussed in this chapter (Sect. 8.2)

The paucity of good data makes it difficult to provide more than minimum relative ages of active rockglaciers. There is a need for better information, though some initial conclusions are already possible.

The earlier chapters of this book have summarized available information on rockglaciers in an analytical manner; in contrast, this chapter is intended to draw these parts together in a synthesis. The different aspects of rockglaciers will be discussed as an important subsystem (and integral parts) of high mountain environments.

Active rockglaciers are the visible expression of the creep of mountain permafrost. Thus, they are truly periglacial features despite suggestions, still repeated, that they belong at least partly in the glacial realm. This view cannot be confirmed and adds only confusion to basic research. It is derived from a failure to differentiate between thermal conditions, material properties and rheology as defining characteristics. Permafrost, including mountain permafrost and its creep, is generally defined by its temperature; below 0°C for more than 1 year (or two winters and the intervening summer). In contrast, glaciers are primarily defined by their movement and not by material properties (petrology and structure of the ice contained in them). If ice patches do not move they are called glacierets. Both, rockglaciers and glaciers, are, therefore, quite different features. The first are determined by thermal boundary conditions, the second by a surples of snow accumulation versus melting and sublimation of snow at the surface.